SharedPreferences的创建

有下边3种方式，一种是用系统默认的，一种自己起个名字

PreferenceManager.getDefaultSharedPreferences(context)

context.getSharedPreferences("name", Context.MODE_PRIVATE);

activity.getPreferences(Context.MODE_PRIVATE)

那么这个文件在哪里？
/data/data/"+getPackageName()+"/shared_prefs/name.xml

系统默认生成的那个文件名字是这样的context.getPackageName() + "_preferences"

    public static SharedPreferences getDefaultSharedPreferences(Context context) {
        return context.getSharedPreferences(getDefaultSharedPreferencesName(context),
                getDefaultSharedPreferencesMode());
    }

    private static String getDefaultSharedPreferencesName(Context context) {
        return context.getPackageName() + "_preferences";
    }

activity下的名字,就是这个activity的类名，不带路径的

    /**
     * Retrieve a {@link SharedPreferences} object for accessing preferences
     * that are private to this activity.  This simply calls the underlying
     * {@link #getSharedPreferences(String, int)} method by passing in this activity's
     * class name as the preferences name.
     */
    public SharedPreferences getPreferences(int mode) {
        return getSharedPreferences(getLocalClassName(), mode);
    }

    /**
     * Returns class name for this activity with the package prefix removed.
     * This is the default name used to read and write settings.
     *
     * @return The local class name.
     */
    @NonNull
    public String getLocalClassName() {
        final String pkg = getPackageName();
        final String cls = mComponent.getClassName();
        int packageLen = pkg.length();
        if (!cls.startsWith(pkg) || cls.length() <= packageLen
                || cls.charAt(packageLen) != '.') {
            return cls;
        }
        return cls.substring(packageLen+1);
    }

看一下存储的文件长啥样

<?xml version='1.0' encoding='utf-8' standalone='yes' ?>
<map>    
<int name="key2" value="2222" />    
<float name="key5" value="22.4" />    
<long name="key4" value="3333" />    
<string name="key1">aaaa</string>    
<boolean name="key3" value="true" />
</map>

打印xml文件的方法

    try {
        File bb=new File("/data/data/"+getPackageName()+"/shared_prefs/bbb.xml");
        FileInputStream fileInputStream=new FileInputStream(bb);
        BufferedReader bReader=new BufferedReader(new InputStreamReader(fileInputStream));
        StringBuffer sBuffer=new StringBuffer();
        String line;
        while((line=bReader.readLine())!=null) {
            sBuffer.append(line);
        }
        System.out.println("===file======="+sBuffer.toString());
        fileInputStream.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

几个问题

1. sp如果想要改名字咋办

这个其实比较简单,使用File的rename即可

      File file=new File("/data/data/"+getPackageName()+"/shared_prefs/aaa.xml");
    boolean result=file.renameTo(new File("/data/data/"+getPackageName()+"/shared_prefs/bbb.xml"));

2. 如果要把一个sp的数据复制到另一个sp咋办

关键是取出来的value，我们得先判断它的类型才能操作比较麻烦。
所以就把key和value都取出来放到集合里，然后根据value的类型，用对应的put方法存到新的sp里边

  public static void copyOldSP2NewSP(Context context) {
    SharedPreferences sp_old= context.getSharedPreferences("xxxx", 0);
    if(sp_old.getAll().size()==0) {
      Log.d(TAG, "copyOldSP2NewSP ========old have been cleared.");
      return;
    }
    SharedPreferences sp_new=  PreferenceManager.getDefaultSharedPreferences(context);
    ArrayList<String>  listkey=new ArrayList<String>();
    ArrayList<Object>  listValue=new ArrayList<Object>();
    try {
      Map<String, ?> map=sp_old.getAll();
      Set<String> set=map.keySet();
      Iterator<String> keys=  set.iterator();
      //StringBuffer sBuffer=new StringBuffer();
      while(keys.hasNext()) {
        String key=keys.next();
        //sBuffer.append(key+" , ");
        listkey.add(key);
      }
      
      //System.out.println("keys====="+sBuffer.toString());
      
      Collection<?> collection= map.values();
      //StringBuffer  sBuffer2=new StringBuffer();
      Iterator<?> values= collection.iterator();
        while (values.hasNext()) {
          Object value=values.next();
          listValue.add(value);
          //sBuffer2.append(value+" , ");
        }
        //System.out.println("values==============="+sBuffer2.toString());
      
      Editor editor=sp_new.edit();
      for(int i=0;i<listkey.size();i++) {
        String key=listkey.get(i);
        Object value=listValue.get(i);
        save(editor, key, value);
      }
      editor.commit();
      //clear old sharedPreference
      sp_old.edit().clear().commit();
    } catch (Exception e) {
      e.printStackTrace();
      Log.d(TAG, "copyOldSP2NewSP error==="+e.getMessage());
    }
  }

save方法如下

  private void save(Editor editor,String key,Object value) {
      if (value instanceof Integer) {                
          editor.putInt(key, (Integer) value);            } 
      else if (value instanceof Boolean) {                
          editor.putBoolean(key, (Boolean) value);            } 
      else if (value instanceof String) {               
          editor.putString(key, (String) value);            } 
      else if (value instanceof Float) {                
          editor.putFloat(key, (Float) value);            } 
      else if (value instanceof Long) {                
          editor.putLong(key, (Long) value);
      }
  }

最后说下

如下，我们哪怕新弄一个xxxx的sp，那么keyset也不是null，所以可以不用做空判断，只需要判断size是否是0即可。
getSharedPreferences("xxxx", 0).getAll().keySet()

studio或者eclipse的日志打印，需要了解下，它一次能打印的字符串最长就4035个，如果你要打印的string长度有个1万，那么只显示4035个，